In general, the improvement of air permeability resistance is designed for a rubber composition used for an inner liner.
Butyl rubbers such as a butyl rubber and a chlorinated butyl rubber that does not allow air to pass through easily have been conventionally used for producing a rubber composition (rubber composition for an inner liner) used for the inner liner of a tire.
However, although it is considered that a butyl rubber gauge is thickened in order to improve the air permeability resistance, a halogenated butyl rubber used is precious; therefore when a lot of the butyl rubber is used, the production cost of a tire is increased and the light weighting of the tire is not designed. Further, when the fluctuation of the finishing rubber gauge is wide even if the butyl rubber gauge is thickened, there is also generated possibility that air deflates from the thinnest portion of the rubber gauge.
In Japanese Unexamined Patent Publication No. 2005-264114, there is disclosed a rubber composition capable of being used for an inner liner that is obtained by using a specific amount of a halogenated butyl rubber as a rubber component and dividedly kneading zinc oxide with it, in order to make a tire be light weight by thinly keeping the rubber gauge of an inner liner without lowering viscosity in the production step of a tire. However, it is susceptible to improvement with respect to a point that the Mooney viscosity of the rubber composition is controlled and a predetermined gauge is retained at a site at which a gauge is most necessary.
In Japanese Unexamined Patent Publication No. 2006-89526, there is disclosed a rubber composition capable of being used for an inner liner that is obtained by compounding specific amounts of silica, calcium carbonate and carbon black with a rubber component comprising a natural rubber and/or its modified article, in order to provide a tire keeping air permeability resistance and crack growth resistance performance by improving processability at the production of a rubber composition for a tire and using the obtained rubber composition for a tire, for an inner liner. However, it is susceptible to improvement with respect to a point that since the Mooney viscosity is too high, it cannot be used for a usual tire.
In Japanese Unexamined Patent Publication No. 2006-249147, there is disclosed a rubber composition capable of being used for an inner liner that includes a rubber component comprising a natural rubber, silica with low BET specific surface area (nitrogen adsorption specific surface area) and carbon black, in order to improve the rolling resistance of a tire and improve processability. However, it is susceptible to improvement with respect to a point that since the Mooney viscosity is similarly too high, it cannot be used for a usual tire.